1. Field of the Invention
The present invention relates to a signal processing method for a magnetic disk drive, an optical disk drive, and the like, and in particular, to a signal processing method capable of improving data reliability in data recovery.
2. Description of the Related Art
Signal processing apparatuses such as a disk drive recently utilize a partial response maximum likelihood (PRML) data detecting method, which makes it possible to obtain a desired data error rate with a low signal-to-noise ratio. A representative PRML data detecting method for a magnetic disk drive has been described in pages 454 to 461 of “Viterbi Detection of Class IV Partial Response on a Magnetic Recording Channel” written by Roger W. Wood in “IEEE Transactions on Communications, Vol. Com-34, No. 5, May 1986. Additionally, as described in JP-A-7-201135 and JP-A-8-116275, an Extended PRML (EPRML) data detecting method has been adopted to reproduce signals with a lower signal-to-noise ratio. To sample signal waveforms in the PRML signal detection method, a phase locked loop circuit is used as described in JP-A-1-143447 and JP-A-2-2719. Recently, an interpolated timing recovery (ITR) circuit as described in JP-A-9-231506 has been proposed to produce synchronized target sample data from asynchronously sampled data.
FIG. 38 shows an example of structure of a general magnetic disk drive employing the PRML data detection method. A magnetic recording media 54 is a circular rotating magnetic recording media and is used to record data from host processor. In the media 54, data track information and sampled servo information are located in order to achieve appropriate date recording and reproducing processing, as shown in FIG. 39. Data track information stores data from host processor. Data recording and reproducing processor is carried out for each block called “sector” on tracks concentrically formed on the media 54. Sampled Servo information, which follow the head 53 to appropriate track, is recorded on the media 54 in a fixed interval. To follow the head 53 on rotating track, a servo control circuit 52 positions head 53 in accordance with servo information. The other constituent components of FIG. 38 are disposed for the recording/reproducing of data from host processor and operate as following.
Recording process is started by a write instruction from host processor. The instruction is received by a microprocessor 55 through a controller 51. Microprocessor 55 issues write control command to controller 51 and servo controller 52. Controller 51 temporarily stores record data following the write instruction in a random access memory (RAM) 56. Servo controller 52 moves head 53 to a predetermined track, which is assigned in the write instruction. After head 53 is completely positioned to the track, the data temporarily recorded in RAM 56 is sent to a recorder circuit 58 together with a sync signal necessary for reproduction of the data and an error correction code (ECC) generated by an ECC generating and correcting circuit 57. Recorder circuit 58 modulates the write data stream based on a PRML data detection method. Resultantly, the write data stream is written via a read/write (RW) amplifier 59 and head 53 in a sector of the predetermined track.
On the other hand, reproducing of data from a magnetic disk drive is commenced by a read instruction of host controller. On receiving the read instruction, microprocessor 55 issues a read control command to servo controller 52 and controller 51. Servo controller 52 moves head 53 to a track in which specified data is recorded. When head 53 is positioned to the specified track, controller 51 instructs a reproducer circuit 60 to initiate reading data. A read data stream of the target sector recorded on media 54 is transmitted as reproducing signals via head 53 and RW amplifier 59 to reproducer circuit 60. In accordance with the sync signal added to the data in the recording thereof, reproducer circuit 60 produces read data synchronized with the reproducing signals. Using sampled signals synchronized with the reproducing signals, a PRML-data detection circuit demodulates read data. The read data is temporarily stored in RAM 56. ECC circuit 57 checks and corrects errors of the read data. When the data has no errors or correctable errors by using ECC circuit 57, the data is transferred as reproduced data to the host processor. When ECC circuit 57 cannot correct all errors, microprocessor 55 retries read operation while using variable control parameters until the data can be correctly reproduced. Finally, the trusted data in RAM 56 is transferred via controller 51 to the host processor. Otherwise, a reproduction error is notified thereto. In addition to the recording and reproducing of data, the system conducts a dropout detecting operation to detect a position and length of dropout on media. And also, the system conducts optimization of circuit parameters to change characteristics of recorder and reproducer circuits 58 and 60.
Magnetic recording and reproducing apparatuses of the conventional technology achieves data recording and reproducing operations in the configuration described above.
In the recording and reproducing operations, when read data has correctable errors by using ECC circuit 57, the corrected data is immediately transferred to the host processor. However read data has uncorrectable errors exceeded correction capability of the ECC circuit 57, magnetic recording and reproducing apparatuses retries read operation from the sector on media 54. Therefore, it needs a wait time to start re-read target sector operation, called read latency. This leads to a problem of disadvantageous elongation in the data access time.
Moreover, a partial missing of record information due to, for example, dropout of a magnetic film of media 54 may cause a miss-lock of phase locked loop circuit. In such a situation, the retry of data reproduction usually fails and hence additional latency is required. Resultantly, the data access time is conspicuously elongated.
In addition, optimization of circuit parameters of the signal processing circuit and surface check of a disk are repeatedly carried out in accordance with reproducing signals from the disk while changing circuit parameters. Resultantly, time for optimization and testing of the magnetic recording and reproducing apparatuses is increased.